Field of the Invention
The present invention relates to image forming apparatus, and more particularly to improvements in devices for erasing charges from the photosensitive member of such apparatus and separating copy paper from the member.
Description of the Prior Art
Image forming apparatus, such as copying machines, have found wide use which comprise a photosensitive drum for forming a toner image on its surface, a transfer corona charger for transferring the toner image to copy paper and a fixing unit for fixing the transferred toner image to the paper. With such apparatus, the copy paper is separated from the photosensitive drum electrostatically by a separating corona charger, or mechanically by a separating belt or pawl.
However, the apparatus incorporating the mechanical separating means has a drawback. For image transfer, the photosensitive drum is charged over the area covered with copy paper and also over areas outside the forward and rear ends of the paper in view of the responsiveness of the transfer corona charger. The charged portion is not discharged immediately after the charging, with the result that toner particles adhering to the cleaning blade or held suspended in the vicinity of the drum are attracted to the charged portion. These toner particles produce an adverse influence on the latent image to be subsequently formed on the photosensitive drum.
To remove the undesirable charges, a charge eraser has been proposed which is positioned free of interference with the copy paper to be transported for removing charges from the photosensitive drum after the separation of copy paper (see, for example, Unexamined Japanese Patent Publication No. 55(1980)-156978).
The eraser becomes soiled with suspended toner particles in the vicinity of the drum and must therefore be cleaned. The eraser which is so disposed as stated above then requires some mechanism for rendering the eraser removable for cleaning. This entails the problem that the power supply connection means for the eraser becomes complex.
When the aforementioned mechanical separating means is used, one side of the copy paper is forcibly removed, and the remaining portion is further removed by a force transmitted through the paper itself from the removed side, against electrostatic attraction between the drum and the paper. Accordingly, the mechanical means has the problem that the copy paper is not separable and transportable smoothly when having low stiffness or a large width.